This application is a national phase application based on PCT/IB01/00544, filed Apr. 2, 2001, and claims the priority of Italian patent application no, TO2000A000333, filed Apr. 7, 2000.
1. Field of the Invention
The present invention relates to a device and method for infusing a liquid in an extracorporeal blood circuit of a dialysis machine.
2. Description of the Related Art
As is well known, blood is composed of a liquid part called blood plasma and a corpuscular part formed by the blood cells, including, among others, the red blood cells. In cases of renal insufficiency, apart from the aforementioned components, the blood also contains metabolic waste (urea, creatinine) in excess which must be removed by means of a dialysis treatment effected by a dialysis machine.
A dialysis machine a generally comprises:
a filter (dialyzer) comprising a blood compartment and a dialysis liquid compartment separated from one another by a semi-permeable membrane
an extracorporeal blood circuit, which is connected to the blood compartment of the filter; and
a dialysis liquid circuit, which is connected to the dialysis liquid compartment of the filter.
In use, the blood to be treated and a dialysis liquid respectively pass through these compartments, generally flowing in counter-current.
During dialysis treatment, there is migration of metabolic waste from the blood compartment to the dialysis liquid compartment through the semipermeable membrane by diffusion. Metabolic waste is also transferred by convection, from the blood compartment to the dialysis liquid compartment, when ultrafiltration of plasma water is caused through the membrane in order that the patient lose a determined weight during the treatment.
To increase the efficiency of dialysis treatment, it is also known to cause the ultrafiltration of large amounts of plasma water, so as to enhance the effects of transport of the undesirable waste by convection. The quantity of plasma water removed in excess relative to the desired final weight loss is compensated with a substitution liquid, which is infused into the extracorporeal blood circuit. The substitution liquid is infused either upstream from the filter (pre-dilution technique) or downstream from the filter (post-dilution technique). The infusion liquid generally consists of a solution with physiological composition and concentration.
Both pre-dilution and post-dilution techniques have their respective advantages and disadvantages.
In the post-dilution technique, the plasma water removed through the membrane is more concentrated than in the pre-dilution technique and, at equal flows, the treatment is more efficient. On the other hand, with the post-dilution technique, blood becomes more easily concentrated, which can slower the blood flow in the filter as well as the ultrafiltration of plasma water (through partial clogging of the filter itself), giving rise to the phenomenon called filter xe2x80x9ccakingxe2x80x9d. Consequently, the post-dilution technique permits extraction of a more limited quantity of plasma water than with the pre-dilution technique.
With the pre-dilution technique, the critical conditions leading to xe2x80x9ccakingxe2x80x9d are avoided and the ultrafiltration efficiency is increased. However, at equal flows, the pre-dilution technique is less efficient than the post-dilution technique.
The aim of the present invention is to provide a device and a method for infusing a liquid into an extracorporeal blood circuit of a dialysis machine that do not have the drawbacks described above.
According to the present invention, a dialysis machine comprises:
a filter having a blood compartment and a dialysis liquid compartment separated by a semi-permeable membrane;
an extracorporeal blood circuit having an arterial pipe connected to an inlet of the blood compartment and a venous pipe connected to an outlet of the blood compartment;
a dialysis liquid circuit having a supply pipe connected to an inlet of the dialysis liquid compartment and a drain pipe connected to an outlet of the dialysis liquid compartment;
a infusion circuit having a pre-dilution pipe connected to the arterial pipe and a post-dilution pipe connected to the venous pipe;
means for varying the flow of an infusion liquid in the pre-dilution pipe and in the post-dilution pipe, and
control means for controlling the flow varying means so that the flow of the infusion liquid in the pre-dilution pipe and the post-dilution pipe matches a determined sequence.
The dialysis machine according to the invention may comprise one or more or the following features:
the control means comprises means for determining the infusion sequence from at least one characteristic value (FF, TMPave, Kuf) correlated with the concentration of the blood (CE) and/or the filtration efficiency of the filter.
the control means comprises means for comparing the characteristic value (FF, TMPave, Kuf) with a series of intervals (I1 . . . x, IT1 . . . x, IK1 . . . x), each interval (I1 . . . x IT1 . . . x, IK1 . . . X) being associated with at least a predetermined control signal (S, G, H, L).
the infusion varying means comprises a valve means for alternately occluding the pre-dilution pipe and the post-dilution pipe, and the predetermined control signal (G) defines a sequence for opening and closing the valve means.
the infusion varying means comprises an infusion pump for circulating the infusion liquid, and the predetermined control signal (L) is for regulating the flow rate (IR) of liquid generated by the infusion pump.
the dialysis machine comprises a ultrafiltration pump for causing ultrafiltration of plasma water through the membrane of the filter, and the predetermined control signal (S) is for regulating the flow rate (UFR) of liquid generated by the ultrafiltration pump.
the dialysis machine comprises a bubble trap connected to the arterial pipe and a bubble trap connected to the venous pipe and means for injecting or withdrawing air into/from the bubble traps so as to adjust the level of liquid therein, and in the predetermined control signal (S) is for controlling the means for injecting or withdrawing air into/from the bubble traps.
the dialysis machine comprises:
means for determining a ultrafiltration flow rate (UFR) of plasma water through the membrane of the filter;
means for determining the haematocrit (Hct) at the inlet of the filter, and
means for calculating the characteristic value as a filtration factor (FF) equal to UFR/[Qb(1xe2x88x92Hct)].
the dialysis machine comprises:
means for measuring the blood pressure values (Pbo, Pbi) at the inlet and at the outlet of the blood compartment of the filter;
means for measuring the dialysis liquid pressure values (Pdi, Pdo) at the inlet and at the outlet of the dialysis liquid compartment of the filter;
means for calculating an inlet transmembrane pressure value (TMPi) as the difference between the pressure value (Pbi) at the inlet of the blood compartment and the pressure value (Pdo) at the outlet of the dialysis liquid compartment and an outlet transmembrane pressure value (TMPo) as the difference between the pressure value (Pbo) at the outlet of the blood compartment and the pressure value (Pdi) at the inlet of the dialysis liquid compartment;
means for calculating the characteristic value as a mean transmembrane pressure value (TMPave) equal to [TMPixe2x88x92TMPo]/2.
the dialysis machine comprises:
means for determining a ultrafiltration flow rate (UFR) of plasma water through the membrane of the filter;
means for calculating the characteristic value as an actual permeability (Kuf) equal to the ratio between the ultrafiltration flow rate (UFR) and the mean transmembrane pressure value (TMPave).
Another object of the present invention is a method for infusing an infusion liquid into an extracorporeal blood circuit of a dialysis liquid machine, the extracorporeal blood circuit having an arterial pipe connected to an inlet of a blood compartment of a filter, and a venous pipe connected to an outlet of the blood compartment, the filter having a blood compartment and a dialysis liquid compartment separated by a semi-permeable membrane,
characterized in that it comprises the steps of;
determining an infusion sequence from at least one characteristic value (FF, TMPave, Kuf) correlated with the concentration of the blood (CE) and/or a filtration efficiency of the filter, and
infusing the infusion solution in either one or both of the arterial pipe and in the venous pipe in accordance with the determined infusion sequence.